Sexuality has an enormous impact on the quality of life of aging men. Numerous studies have shown that the decline in sexual function and frequency of intercourse is strongly related to age, but that many men remain sexually active into their 80s and 90s. Studies also suggest that declines in intercourse and function (and other "objective' aspect of sexual behavior) are often not accompanied by declines in levels of interest or satisfaction (or other 'subjective' aspects). However, none of these studies provide unconfounded estimates of the normative decline in sexual behavior, especially with regard to behavior, especially with regard to behaviors (such as masturbation) that may be substituted for more rigorous activities. With the graying of the American population, these issue should become increasingly important. Indeed, a recent conference on Gender and Human Sexuality sponsored by Columbia University and the NIH strongly recommended additional research on aging and sexual function among non-patient samples. Limitations of current knowledge in the area of older male sexual behavior include: (1) the use of cross-sectional rather than longitudinal data; (2) limited data on a range of sexual behavior outcomes; (3) limited information on variables that may confound the relation of age to sexual behavior; and finally, (4) the use of small, clinic-based, convenience samples. The proposed study will make use of the rich dataset of the longitudinal population-based Massachusetts Make Aging Study to examine trends over a 9-yr period in a range of sexual behavior (e.g., frequency of intercourse, orgasm, erections, and masturbation, as well as sexual fantasies, desire, interest, enjoyment, and expectations). Unlike similar studies, the MMAS database has available information on demographics, health status, physiological measures (hormones, anthropometrics), psychosocial and social status factors, and lifestyles. As proposed, this research will provide the most comprehensive picture to date of the sexual behavior of aging men with respect to its trends over time, what factors contribute to these trends, and whether declines in sexual behavior are associated with sexual dissatisfaction.